Oxidation stable gear oil compositions

ABSTRACT

A gear oil lubricant composition and method of operating a vehicle with the composition. The composition may include a first olefinic lubricant having a viscosity ranging from about 80 centistokes to about 150 centistokes at 100° C. and a second olefinic lubricant having a viscosity ranging from about 2 centistokes to about 15 centistokes at 100° C. A ratio of the first olefinic lubricant to the second olefinic lubricant may range from about 2:1 to about 8:1. Additionally, the composition may include an alkylated naphthalene base oil, a boronated ashless dispersant, at least one hindered phenol antioxidant, at least one alkylated diphenylamine antioxidant, and a gear oil additive package having an active phosphorus content of less than about 700 ppm and an active sulfur content of less than about 3 wt. %. The gear oil lubricant composition may contain less than about 0.1 percent by weight antioxidant composition based on a total weight of the lubricant composition.

FIELD

The present disclosure relates to gear oil compositions, and inparticular to gear oil compositions for severe duty applications thatexhibit improved oxidation stability for extended periods of time.

BACKGROUND

Lubricants are used to reduce wear between moving parts where there ismetal to metal contact and to remove heat from the parts. In someapplications, such as the axles of heavy duty vehicles, the lubricantsmay encounter extreme temperatures in an environment in which they areused. Extreme temperatures and applied loads may result in increasedoxidation of the lubricants thereby increasing the viscosity of thelubricants above a desirable level. As the viscosity increases, thelubricity properties of the lubricants may significantly decrease to thepoint of axle failure.

Accordingly, for severe duty applications where environmentaltemperatures may exceed about 40° C. for extended periods of time andwhere the vehicle load may exceed 25 metric tons, axle lubricants mustbe changed more often than lubricants used in less harsh environments.If the lubricants are not changed on a more frequent schedule, damage tomoving parts relying on lubrication may occur. Until now, lubricants forheavy duty applications, such as GL-5 gear oils, must pass an oxidationstability test according to an ASTM D5704 (L60-1) that is a 50 hourtest. However, such evaluation does not provide lubricants that aresuitable for the severe duties described above. Accordingly, what isneeded is a lubricant for heavy duty applications that can pass an L60-1oxidation stability test of about 300 hours in order to providelubricant replacement intervals of significantly greater than about30,000 kilometers in a severe environment.

SUMMARY OF THE EMBODIMENTS

With regard to the foregoing, the disclosure provides a gear oillubricant composition including a first olefinic lubricant having aviscosity ranging from about 80 centistokes to about 150 centistokes at100° C. and a second olefinic lubricant having a viscosity ranging fromabout 2 centistokes to about 15 centistokes at 100° C. A ratio of thefirst olefinic lubricant to the second olefinic lubricant ranges fromabout 2:1 to about 8:1. Additionally, the composition may include analkylated naphthalene base oil, a boronated ashless dispersant, at leastone hindered phenol antioxidant, at least one alkylated diphenylamineantioxidant, and a gear oil additive package having an active phosphoruscontent of less than about 700 ppm and an active sulfur content of lessthan about 2 weight percent. The gear oil lubricant composition maycontain less than about 0.1 percent by weight antioxidant compositionbased on a total weight of the lubricant composition.

In another embodiment there is provided a thermally stable gear oillubricant composition. The lubricant composition includes a firstolefinic lubricant having a viscosity ranging from about 80 centistokesto about 150 centistokes at 100° C., and a second olefinic lubricanthaving a viscosity ranging from about 2 centistokes to about 15centistokes at 100° C. A ratio of the first polyolefinic lubricant tothe second olefinic lubricant ranges from about 2:1 to about 8:1. Alsoincluded in the composition may be an alkylated naphthalene base oil, aboronated ashless dispersant, an antioxidant composition comprising atleast one hindered phenol antioxidant and at least one alkylateddiphenylamine antioxidant; and a conventional gear oil additive package.With respect thermal stability, the lubricant composition may have acarbon varnish rating of greater than about 7.5 and a sludge rating ofabout 9.4 after an L60-1 oxidative stability test of 300 hours.

In yet another embodiment there is provided a method of operating avehicle containing a drive axle. The method includes providing as alubricant for the drive axle a composition containing a first olefiniclubricant having a viscosity ranging from about 80 centistokes to about150 centistokes at 100° C. and a second olefinic lubricant having aviscosity ranging from about 2 centistokes to about 15 centistokes at100° C. A ratio of the first olefinic lubricant to the second olefiniclubricant ranges from about 2:1 to about 8:1. The composition may alsoinclude an alkylated naphthalene base oil, a boronated ashlessdispersant, an antioxidant composition comprising at least one hinderedphenol antioxidant and at least one alkylated diphenylamine antioxidant,and a conventional gear oil additive package. The lubricant compositionmay have an oxidation stability in a 300 hour oxidation stability testthat provides a viscosity increase of less than about 100%, a carbonvarnish rating of greater than about 7.4, and a sludge rating of greaterthan or equal to about 9.3.

An advantage of compositions according to the disclosure is that heavyduty gear applications using the lubricants exhibit reduce wear and/orfailure without decreasing the lubricant replacement interval. Anotheradvantage is that the lubricant compositions according to the disclosuremay be formulated from commercially available components. The followingdetailed description of embodiments may provide other advantages.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, the term “hydrocarbyl substituent” or “hydrocarbylgroup” is used in its ordinary sense, which is well-known to thoseskilled in the art. Specifically, it refers to a group having a carbonatom directly attached to the remainder of a molecule and having apredominantly hydrocarbon character. Examples of hydrocarbyl groupsinclude:

(1) hydrocarbon substituents, that is, aliphatic (e.g., alkyl oralkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, andaromatic-, aliphatic-, and alicyclic-substituted aromatic substituents,as well as cyclic substituents wherein the ring is completed throughanother portion of the molecule (e.g., two substituents together form analicyclic radical);

(2) substituted hydrocarbon substituents, that is, substituentscontaining non-hydrocarbon groups which, in the context of thedescription herein, do not alter the predominantly hydrocarbonsubstituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy,mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);

(3) hetero-substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this description,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms. Hetero-atoms include sulfur, oxygen, nitrogen, andencompass substituents such as pyridyl, furyl, thienyl, and imidazolyl.In general, no more than two, such as no more than one, non-hydrocarbonsubstituent will be present for every ten carbon atoms in thehydrocarbyl group; typically, there will be one non-hydrocarbonsubstituent in the hydrocarbyl group.

Lubricant compositions according to the disclosure contain a base oilcomponent, an antioxidant composition, an ashless dispersant, and a gearoil additive package. The compositions may be characterized by having anactive sulfur content of from about 1 wt. % to about 3 wt. %, an activephosphorus content of from about 200 to about 700 ppm, and an activenitrogen content of from about 100 to about 700 ppm, typically fromabout 300 to about 500 ppm. The lubricant composition may also becharacterized by having a carbon varnish rating of greater than about7.4 and a sludge rating of greater than about 9.3 after a 300 houroxidation stability test conducted according to ASTM D5704 (L60-1).

Base Oil Component

The base oil component of lubricant compositions according to thedisclosure may include an α-olefin component and a Group V base oilcomponent. Oligomerized α-olefins have been known for many years to beeffective synthetic lubricating oils. For example, U.S. Pat. No.3,149,178 to Hamilton et al., describes oligomers of C₆₋₁₂ α-olefinsmade using a Friedel-Crafts catalyst, a peroxide catalyst or thermaltreatment. The starting olefins are predominantly α-olefins, that is,linear terminal olefins. By predominantly is meant that they containover about 50 mole percent, as a further example, over about 75 molepercent of α-olefins.

It is desirable to use pure α-olefins in the base oil component, butcommercially available α-olefins contain minor amounts of internalolefins and vinylidene olefins. It has been found that in makingdimmers, fairly large amounts of internal olefins can be toleratedwithout adversely affecting the physical properties of the oligomer. Itwould appear that either the α-olefins in the commercial olefins canreact with the internal olefins or that the internal olefins are inequilibrium with α-olefins and that as the α-olefins react, moreinternal olefins are isomerized to α-olefins.

Suitable olefinic oligomers for use as a base oil include hydrogenatedolefin oligomers consisting mainly of dimers of C₆₋₂₀ predominantlyα-olefins having a viscosity above about 3.0 centistokes (cSt) at 100°C. Such oligomers may be made by contacting a C₆₋₂₀ predominantlyα-olefin or mixture thereof with a Friedel-Crafts catalyst at atemperature of about 20° C. to about 200° C. until the reaction mixtureexcluding monomer is predominantly dimer. Representative Friedel-Craftscatalysts are BF₃, BCl₃, AlCl₃, AlBr₃, SnCl4, GaCl₃, and the like. Theproduct is distilled to remove unreacted monomer and then ishydrogenated.

Accordingly, olefins which may be used for making the oligomers aredodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene,and octadecene. When dodecene is used it should be in a mixture ofolefins containing higher olefins, e.g. tetradecene, hexadecane, and thelike. Other suitable olefins used as starting materials contain about 12to about 16 carbon atoms and mixtures thereof with the above statedproviso regarding dodecene.

A relatively low viscosity α-olefin oligomer and a relatively highviscosity α-olefin oligomer make up a predominant amount of the base oilcomponent. By predominant amount is meant that the base oil containsover 50 percent by weight of the low and high viscosity α-olefinoligomers. The α-olefin oligomer having the highest viscosity has akinematic viscosity at 100° C. of about 80 to about 120 cSt. Therelatively low viscosity α-olefin oligomer has a kinematic viscosity at100° C. of about 6 to about 10 cSt. A weight ratio of the high viscosityα-olefin oligomer to the low viscosity α-olefin oligomer in thelubricant composition typically ranges from about 2:1 to about 6:1.

An important component of lubricant compositions according to thedisclosure is a Group V base oil as specified in the American PetroleumInstitute (API) Base Oil Interchangeability Guidelines. A suitable GroupV component is an alkylated aromatic compound. Suitable alkylatedaromatic compounds include alkylated benzenes, alkylated anthracenes,alkylated phenanthrenes, alkylated biphenyls, and alkylated naphthalenesand the like.

Alkylated naphthalenes may be produced by any suitable means known inthe art, from naphthalene itself or from substituted naphthalenes whichmay contain one or more short chain alkyl groups having up to abouteight carbon atoms, such as methyl, ethyl, or propyl, etc. Suitablealkyl-substituted naphthalenes include alpha-methylnaphthalene,dimethylnaphthalene, and ethylnaphthalene. Naphthalene itself issuitable since the resulting mono-alkylated products have better thermaland oxidative stability than the more highly alkylated materials.Alkylated naphthalene lubricant compositions are described in U.S. Pat.No. 3,812,036 to Romine and U.S. Pat. No. 5,602,086 to Le et al. Theproduction of alkylnaphthalenes is disclosed in U.S. Pat. No. 4,714,794to Yoshida et al. A commercially available alkylated naphthalene isavailable from Exxon/Mobil Chemical Company of Houston, Tex. under thetrade name SYNESSTIC® 12.

The amount of alkylated naphthalene component in the lubricantcomposition may range from about 20 to about 35 percent by weight of thetotal weight of the composition. With respect to the α-olefin oligomercomponents, the alkylated naphthalene component is present in a ratio ofα-olefin oligomers to alkylated naphthalene ranging from about 1.5:1 toabout 2.5:1.

Antioxidant Component

The antioxidant component of the lubricant compositions includes atleast two antioxidant compounds, i.e., a hindered phenol antioxidant andan aromatic amine antioxidant. Illustrative examples of stericallyhindered phenolic antioxidants include orthoalkylated phenolic compoundssuch as 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol,2,4,6-tri-tert-butylphenol, 2-tert-butylphenol, 2,6-diisopropylphenol,2-methyl-6-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol,4-(N,N-dimethylamino-methyl)-2,8-di-tert-butylphenol,4-ethyl-2,6-di-tert-butylphenol, 2-methyl-6-styryl-phenol,2,6-distyryl-4-nonylphenol, and their analogs and homologs. Mixtures oftwo or more of the foregoing phenolic compounds are also be used as thefirst antioxidant compound.

Aromatic amine antioxidant compounds include aromatic secondarymonoamines and aromatic secondary polyamines. Illustrative aromaticsecondary monoamines include diphenylamine, alkyl diphenylaminescontaining 1 or 2 alkyl substituents each having up to about 16 carbonatoms, phenyl-t-naphthylamine, phenyl-β-naphthylamine, alkyl- oraralkylsubstituted phenyl-β-naphthylamine containing one or two alkyl oraralkyl groups each having up to about 16 carbon atoms, alkyl- oraralkylsubstituted phenyl-β-naphthylamine containing one or two alkyl oraralkyl groups each having up to about 16 carbon atoms, and similarcompounds.

A suitable type of aromatic amine antioxidant is an alkylateddiphenylamine of the general formulaR¹—C₆—H₄—NH—C₆—H₄—R²wherein R¹ is an alkyl group (for example, a branched alkyl group)having about 8 to about 12 carbon atoms (as another example, about 8 orabout 9 carbon atoms) and R² is a hydrogen atom, alkylaryl or an alkylgroup (such as a branched alkyl group) having about 8 to about 12 carbonatoms, (as another example, about 8 or about 9 carbon atoms). Suitablecompounds are available commercially from Crompton Corporation ofMiddlebury, Conn. under the trade names NAUGALUBE® 438L, 640, and 680.Other commercially available aromatic amine antioxidants includecompounds available from R. T. Vanderbilt Company, Inc. of Norwalk,Conn. under the trade names VANLUBE® SL, DND, NA, 81, 961, and 2005.

The amount of antioxidant component in lubricant compositions describedherein may be less than about 0.5 percent by weight of the total weightof lubricant composition. Typically, the antioxidant component may rangefrom about 0.05 to about 0.25 weight percent based on the total weightof the lubricant composition. Of the total amount of antioxidantcomponent, the hindered phenolic antioxidant may be present in an amountthat ranges from about 0.70 to about 1.30 times the amount of aromaticamine antioxidant in the lubricant composition. A suitable antioxidantmay contain about 50 wt. % hindered phenolic antioxidant and 50 wt. %aromatic amine antioxidant.

Ashless Dispersant component

The ashless dispersant of the lubricant compositions described hereinmay be selected from any of the ashless dispersants known to thoseskilled in the art. A suitable ashless dispersant is ahydrocarbyl-substituted succinimide dispersant which is post-treated toprovide a boronated or boronated/phosphorylated dispersant.

Hydrocarbyl-substituted succinic acylating agents are used to makehydrocarbyl-substituted succinimides. The hydrocarbyl-substitutedsuccinic acylating agents include, but are not limited to,hydrocarbyl-substituted succinic acids, hydrocarbyl-substituted succinicanhydrides, the hydrocarbyl-substituted succinic acid halides(especially the acid fluorides and acid chlorides), and the esters ofthe hydrocarbyl-substituted succinic acids and lower alcohols (e.g.,those containing up to about 7 carbon atoms), that is,hydrocarbyl-substituted compounds which can function as carboxylicacylating agents.

Hydrocarbyl substituted acylating agents are made as by reacting apolyolefin or chlorinated polyolefin of appropriate molecular weightwith maleic anhydride. Similar carboxylic reactants can be used to makethe acylating agents. Such reactants may include, but are not limitedto, maleic acid, fumaric acid, malic acid, tartaric acid, itaconic acid,itaconic anhydride, citraconic acid, citraconic anhydride, mesaconicacid, ethylmaleic anhydride, dimethylmaleic anhydride, ethylmaleic acid,dimethylmaleic acid, hexylmaleic acid, and the like, including thecorresponding acid halides and lower aliphatic esters.

Hydrocarbyl-substituted succinic anhydrides are conventionally preparedby heating a mixture of maleic anhydride and an aliphatic olefin at atemperature of from about 175° C. to about 275° C. The molecular weightof the olefin can vary depending upon the intended use of thesubstituted succinic anhydrides. Typically, the substituted succinicanhydrides will have a hydrocarbyl group of from about 8-500 carbonatoms. However, substituted succinic anhydrides used to make lubricatingoil dispersants will typically have a hydrocarbyl group of about 40-500carbon atoms. Dispersants having a hydrocarbyl group containing fromabout 8 to about 150 carbon atoms are referred to herein as “relativelylow molecular weight dispersants.” Whereas dispersants having ahydrocarbyl group containing more than about 150 carbon atoms up toabout 500 carbon atoms are referred to herein as “relatively highmolecular weight dispersants.” With the very high molecular weightsubstituted succinic anhydrides, it is more accurate to refer to numberaverage molecular weight (Mn) since the olefins used to make thesesubstituted succinic anhydrides may include a mixture of differentmolecular weight components resulting from the polymerization of lowmolecular weight olefin monomers such as ethylene, propylene andisobutylene.

The mole ratio of maleic anhydride to olefin can vary widely. It mayvary, for example, from about 5:1 to about 1:5, as another example, fromabout 1:1 to about 3:1. With olefins such as polyisobutylene having anumber average molecular weight of about 500 to about 7000, as a furtherexample about 800 to about 3000 or higher and the ethylene-alpha-olefincopolymers, the maleic anhydride may be used in stoichiometric excess,e.g. about 1.1 to about 3 moles maleic anhydride per mole of olefin. Theunreacted maleic anhydride can be vaporized from the resultant reactionmixture.

The hydrocarbyl-substituted succinic anhydrides include polyalkyl orpolyalkenyl succinic anhydrides prepared by the reaction of maleicanhydride with the desired polyolefin or chlorinated polyolefin, underreaction conditions well known in the art. For example, such succinicanhydrides may be prepared by the thermal reaction of a polyolefin andmaleic anhydride, as described in U.S. Pat. Nos. 3,361,673; 3,676,089;and 5,454,964. Alternatively, the substituted succinic anhydrides can beprepared by the reaction of chlorinated polyolefins with maleicanhydride, as described, for example, in U.S. Pat. No. 3,172,892. Afurther discussion of hydrocarbyl-substituted succinic anhydrides can befound, for example, in U.S. Pat. Nos. 4,234,435; 5,620,486 and5,393,309. Typically, these hydrocarbyl-substituents will contain fromabout 40 to about 500 carbon atoms.

Polyalkenyl succinic anhydrides may be converted to polyalkyl succinicanhydrides by using conventional reducing conditions such as catalytichydrogenation. For catalytic hydrogenation, a suitable catalyst ispalladium on carbon. Likewise, polyalkenyl succinimides may be convertedto polyalkyl succinimides using similar reducing conditions.

The polyalkyl or polyalkenyl substituent on the succinic anhydridesemployed herein is generally derived from polyolefins which are polymersor copolymers of mono-olefins, particularly 1-mono-olefins, such asethylene, propylene, and butylene. For example, the mono-olefin employedwill have about 2 to about 24 carbon atoms, and as a further example,about 3 to about 12 carbon atoms. Suitable mono-olefins includepropylene, butylene, particularly isobutylene, 1-octene, and 1-decene.Polyolefins prepared from such mono-olefins include polypropylene,polybutene, polyisobutene, and the polyalphaolefins produced from1-octene and 1-decene.

In some embodiments, the ashless dispersant may include one or morealkenyl succinimides of an amine having at least one primary amino groupcapable of forming an imide group. The alkenyl succinimides may beformed by conventional methods such as by heating an alkenyl succinicanhydride, acid, acid-ester, acid halide, or lower alkyl ester with anamine containing at least one primary amino group. The alkenyl succinicanhydride may be made readily by heating a mixture of polyolefin andmaleic anhydride to about 180° C. to about 220° C. The polyolefin may bea polymer or copolymer of a lower monoolefin such as ethylene,propylene, isobutene, and the like, having a number average molecularweight in the range of about 900 to about 3000 as determined by gelpermeation chromatography (GPC).

Amines which may be employed in forming the ashless dispersant includeany that have at least one primary amino group which can react to forman imide group and at least one additional primary or secondary aminogroup and/or at least one hydroxyl group. A few representative examplesare: N-methyl-propanediamine, N-dodecylpropanediamine,N-aminopropyl-piperazine, ethanolamine, N-ethanol-ethylenediamine, andthe like.

Boronated dispersants may be formed by boronating (borating) an ashlessdispersant having basic nitrogen in the molecule. The boronateddispersant may contain at least one polyalkylene moiety. As a furtherexample, the boronated dispersant may include at least two polyalkylenemoieties. The polyalkylene moiety may have a molecular weight of fromabout 900 weight average molecular weight to about 3000 weight averagemolecular weight. The polyalkylene moiety, for example, may have amolecular weight of from about 1300 weight average molecular weight toabout 2100 weight average molecular weight. As a further example, thepolyalkylene moiety may have a molecular weight of about 2100 weightaverage molecular weight. The polyalkylene moiety may include apolybutenyl group. Methods that can be used for boronating the varioustypes of ashless dispersants described above are described for examplein U.S. Pat. Nos. 3,087,936; 3,254,025; 3,281,428; 3,282,955; 2,284,409;2,284,410; 3,338,832; 3,344,069; 3,533,945; 3,658,836; 3,703,536;3,718,663; 4,455,243; and 4,652,387.

The boronated dispersant may include a high molecular weight dispersanttreated with boron such that the borated dispersant includes up to about1 wt. % of boron. As another example the boronated dispersant mayinclude from about 0.7 wt %/o or less of boron. As a further example,the borated dispersant may include from about 0.1 to about 0.7 wt % ofboron. As an even further example, the boronated dispersant may includefrom about 0.25 to about 0.7 wt % of boron. As a further example, theboronated dispersant may include from about 0.35 to about 0.7 wt % ofboron. The dispersant may be dissolved in oil of suitable viscosity forease of handling. It should be understood that the weight percentagesgiven here are for neat dispersant, without any diluent oil added.

The boronated dispersant may be further reacted with an organic acid, ananhydride, and/or an aldehyde/phenol mixture. Such a process may enhancecompatibility with elastomer seals, for example. The boronateddispersant may further include a mixture of boronated dispersants. As afurther example, the boronated dispersant may include anitrogen-containing dispersant and/or may be free of phosphorus.

The boronated dispersant may be present in the lubricant composition inan amount of about 1 wt. % to about 5 wt. %. Further, the fluid mayinclude from about 1.25 wt % to about 3 wt % of the borated dispersant.Further, the fluid may include from about 1.5 wt % to about 2.5 wt % ofthe boronated dispersant. Further, the lubricant composition may includean amount of the boronated dispersant sufficient to provide up to 250parts per million (ppm) by weight of boron in the finished composition,such as for example, from about 50 to about 250 ppm by weight of boronin the finished composition.

Phosphorylated dispersants may be formed by treating an ashlessdispersant with an inorganic phosphorus acid or anhydride. Usefulphosphorus acids or anhydrides which may be useful in forming thepost-treated ashless dispersant include phosphorous acid (H₃PO₃),phosphoric acid, hypophosphoric acid, phosphorus trioxide (P₂O₃),phosphorus tetraoxide (P₂O₄), and phosphoric anhydride (P₂O₅). Mixturesof two or more such compounds can be used. Illustrative examples ofdihydrocarbyl hydrogen phosphites which may be reacted with the basicnitrogen-containing dispersants for the purposes of this invention,include diethyl hydrogen phosphite, dibutyl hydrogen phosphite,di-2-ethylhexyl hydrogen phosphite, didecyl hydrogen phosphite,dicyclohexyl hydrogen phosphite, diphenyl hydrogen phosphite, isopropyloctyl hydrogen phosphite, ditetradecyl hydrogen phosphite, dibenzylhydrogen phosphite, and the like. Normally the hydrocarbyl groups willeach contain up to about 30 carbon atoms. Mixtures of two or more suchphosphites can be employed. Dibutyl hydrogen phosphite is a suitabledihydrocarbyl phosphite. Among the monohydrocarbyl-phosphites which canbe utilized in the practice of this invention include such compounds asmonomethyl phosphite, monoethyl phosphite, monobutyl phosphite,monohexyl phosphite, monocresyl phosphite, monobenzyl phosphite,monoallyl phosphite, and the like, and mixtures of two or more suchcompounds. The hydrocarbyl group will normally contain up to about 30carbon atoms. Mixtures of monohydrocarbyl and dihydrocarbyl phosphitesare also suitable, as are the trihydrocarbyl phosphites and the sulfuranalogs of the foregoing phosphites. Phosphorylated ashless dispersantsare described for example in U.S. Pat. No. 5,171,466.

The ashless dispersant component may also be glycolated by reacting asuccinimide with glycolic acid as described in U.S. Pat. No. 5,235,067.

A particularly suitable ashless dispersant is available from AftonChemical Corporation of Richmond, Va. under the trade name HiTEC® 637.

Gear Oil Additive Package Component

Another component of the gear oil lubricant composition according to thedisclosure is a gear oil additive package. The gear additive packagetypically contains one or more of the following additives: corrosioninhibitors, extreme pressure additives, anti-wear additives, rustinhibitors, defoamers, and a process oil. The gear additive package maybe, although it does not have to be, a fully-formulated gear additivepackage, such as a package meeting the requirements for API GL-5 and/orAPI MT-1 and/or MIL-PRF-2105E and/or AGMA 9005-D94. The type and amountof the components present in the gear additive package will depend onthe intended final use of the product. The gear additive package istypically present in an amount of from about 2 to about 25 weightpercent, based on the total weight of the lubricant composition.

A suitable gear oil additive package is available from Afton ChemicalCorporation under the trade name HiTEC® 340.

Extreme Pressure Agent

Various types of sulfur-containing extreme pressure agents may be usedin the gear oil additive package. Examples include dihydrocarbylpolysulfides; sulfurized olefins; sulfurized fatty acid esters of bothnatural and synthetic origins; trithiones; sulfurized thienylderivatives; sulfurized terpenes; sulfurized oligomers of C₂-C₈monoolefins; and sulfurized Diels-Alder adducts such as those disclosedin U.S. reissue patent Re 27,331. Specific examples include sulfurizedpolyisobutene, sulfurized isobutylene, sulfurized diisobutylene,sulfurized triisobutylene, dicyclohexyl polysulfide, diphenylpolysulfide, dibenzyl polysulfide, dinonyl polysulfide, and mixtures ofdi-tert-butyl polysulfide such as mixtures of di-tert-butyl trisulfide,di-tert-butyl tetrasulfide and di-tert-butyl pentasulfide, among others.Combinations of such categories of sulfur-containing extreme pressureagents can also be used, such as a combination of sulfurized isobutyleneand di-tert-butyl trisulfide, a combination of sulfurized isobutyleneand dinonyl trisulfide, a combination of sulfurized tall oil anddibenzyl polysulfide. The amount of extreme pressure agent in the gearoil additive package may range from about 75 to about 95 percent byweight of the total weight of the additive package. In terms of activesulfur content in the lubricant compositions, the lubricant compositionmay contain from about 1 wt. % to about 3 wt. % active sulfur.

Antiwear Agents

The antiwear agents may be phosphorus-containing antiwear agents whichmay include an organic ester of phosphoric acid, phosphorous acid, or anamine salt thereof. For example, the phosphorus-containing antiwearagent may include one or more of a dihydrocarbyl phosphite, atrihydrocarbyl phosphite, a dihydrocarbyl phosphate, a trihydrocarbylphosphate, any sulfur analogs thereof, and any amine salts thereof. As afurther example, the phosphorus-containing antiwear agent may include atleast one of dibutyl hydrogen phosphite (such as HiTEC® 528 antiwearagent available from Afton Chemical Corporation of Richmond, Va.) and anamine salt of sulfurized dibutyl hydrogen phosphite (such as HiTEC® 833antiwear agent available from Afton Chemical Corporation).

The phosphorus-containing antiwear agent may be present in an amountsufficient to provide about 200 to about 700 parts per million by weightof phosphorus in the lubricant composition. As a further example, thephosphorus-containing antiwear agent may be present in an amountsufficient to provide about 150 to about 450 parts per million by weightof phosphorus in the lubricant composition.

The gear oil additive package component may include from about 1 wt % toabout 10 wt % of the phosphorus-containing antiwear agent. As a furtherexample, the gear oil additive package component may include from about3 wt % to about 8 wt % of the phosphorus-containing antiwear agent. Asan example, the gear oil additive package may include from about 4.5 wt% to about 5.5 wt % of an amyl acid phosphate.

Corrosion inhibitors

Copper corrosion inhibitors used in the gear oil additive package mayinclude thiazoles, triazoles, and thiadiazoles. Examples includebenzotriazole, tolytriazole, octyltriazole, decyltriazole,dodecyltriazole, 2-mercaptobenzothiazole,2,5-dimercapto-1,3,4-thiadiazole,2-mercapto-5-hydrocarbylthio-1,3,4-thiadiazoles,2-mercapto-5-hydrocarbyldithio-1,3,4-thiadiazoles,2,5-bis(hydrocarbylthio)-1,3,4-thiadiazoles, and2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazoles. Suitable compoundsinclude the 1,3,4-thiadiazoles, especially the2-hydrocarbyldithio-5-mercapto-1,3,4-dithiadiazoles and the2,5-bis(hydrocarbyldithio)-1,3,4-thiadiazoles, a number of which areavailable as articles of commerce. Other suitable inhibitors of coppercorrosion include ether amines; polyethoxylated compounds such asethoxylated amines, ethoxylated phenols, and ethoxylated alcohols;imidazolines; and the like. See, for example, U.S. Pat. Nos. 3,663,561and 4,097,387. Concentrations of up to about 5 wt. % in the gear oiladditive package component are typical. Suitable copper corrosioninhibitors include ashless dialkyl thiadiazoles. One example of acommercially available ashless dialkyl thiadiazole is HiTEC® 4313corrosion inhibitor, available from Afton Chemical Corporation.

Rust Inhibitors

Rust inhibitors are another inhibitor additive typically included in thegear oil additive package. Such materials include monocarboxylic acidsand polycarboxylic acids. Examples of suitable monocarboxylic acids areoctanoic acid, decanoic acid and dodecanoic acid. Suitablepolycarboxylic acids include dimer and trimer acids such as are producedfrom such acids as tall oil fatty acids, oleic acid, linoleic acid, orthe like. Products of this type are currently available from variouscommercial sources, such as, for example, the dimer and trimer acidssold under the HYSTRENE trademark by the Humko Chemical Division ofWitco Chemical Corporation and under the EMPOL trademark by HenkelCorporation.

Another useful type of rust inhibitor which may be used is comprised ofthe alkenyl succinic acid and alkenyl succinic anhydride corrosioninhibitors such as, for example, tetrapropenylsuccinic acid,tetrapropenylsuccinic anhydride, tetradecenylsuccinic acid,tetradecenylsuccinic anhydride, hexadecenylsuccinic acid,hexadecenylsuccinic anhydride, and the like. Also useful are the halfesters of alkenyl succinic acids having about 8 to about 24 carbon atomsin the alkenyl group with alcohols such as the polyglycols.

Still other suitable rust inhibitors include ether amines; acidphosphates; amines; polyethoxylated compounds such as ethoxylatedamines, ethoxylated phenols, and ethoxylated alcohols; imidazolines;aminosuccinic acids or derivatives thereof, and the like. Materials ofthese types are available as articles of commerce. Mixtures of such rustinhibitors may be used. The amount of rust inhibitor in the gear oiladditive package component may range from about 2 to about 8 weightpercent based on the total weight of the gear oil additive package.

Antifoam agents

A foam inhibitor forms another component of the gear oil additivepackage. Foam inhibitors may be selected from silicones, polyacrylates,surfactants, and the like. One suitable acrylic defoamer material isPC-2244 available from Monsanto Company. The amount of antifoam agent inthe gear oil additive package may range from about 0.5 to about 2.0weight percent based on the total weight of the gear oil additivepackage.

Process Oil

The process oil used in the gear oil additive package may be a naturaloil, a mineral oil, or a blend of such oils. The oil can be paraffinic,naphthenic, or a blend of mineral oils. Pursuant to an embodiment, theprocess oil is a 60 Neutral mineral oil. The process oil is present inthe gear oil additive package in an amount sufficient to solubilize thecomponents of the additive package. Typically, the additive package willcontain from about 2 to about 10 percent by weight of the process oil.

The following non-limiting example is given to illustrate aspects of thedisclosed embodiments. The example is not intended to limit theembodiments as disclosed herein.

EXAMPLE

A gear oil lubricant (Sample 1) was formulated as follows: ComponentWeight Percent 8 cSt polyalphaolefin base oil 11.59 100 cStpolyalphaolefin base oil 47.00 alkylated naphthalene base oil 28.00 sealswell agent 8.00 gear oil additive package 4.00 boronated ashlessdispersant 1.31 hindered phenol antioxidant 0.03 alkylated diphenylamineantioxidant 0.03 Process oil 0.04

The above gear oil formulation had a viscosity grade of 80W-140, and wastested 300 hours for thermal and oxidative stability according to theASTM D 5704 (L-60-1) using the SAE J2360 procedure. The results aregiven in the following table. SAE J2360 Sample 1 Oxidation StabilityTest (L-60-1) 50 hours 300 hours Viscosity Rise (%) 100 Max. 89.24Pentane Insolubles (wt. %) 3.0 Max. −0.86 Toluene Insolubles (wt. %) 2.0Max. 0.06 Carbon Varnish (Rating) 7.5 Min. 8.30 Sludge (Rating) 9.4 Min.9.47

From the foregoing table, it is evident that a gear oil lubricantaccording to the disclosed embodiments may provide superior performancein harsh environments as it is able to provide a relatively lowviscosity increase, and relatively high sludge and carbon varnishratings over extended periods of time. It is expected that a gear oilformulation as disclosed herein will provide extended drain intervalswithout causing excessive wear of vehicle components such as axles.

At numerous places throughout this specification, reference has beenmade to a number of U.S. Patents. All such cited documents are expresslyincorporated in full into this disclosure as if fully set forth herein.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. As used throughout the specificationand claims, “a” and/or “an” may refer to one or more than one. Unlessotherwise indicated, all numbers expressing quantities of ingredients,properties such as molecular weight, percent, ratio, reactionconditions, and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the invention are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard deviation foundin their respective testing measurements. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

1. A gear oil lubricant composition comprising: a first olefiniclubricant having a viscosity ranging from about 80 centistokes to about150 centistokes at 100° C.; a second olefinic lubricant having aviscosity ranging from about 2 centistokes to about 15 centistokes at100° C., wherein a ratio of the first olefinic lubricant to the secondolefinic lubricant ranges from about 2:1 to about 8:1; an alkylatednaphthalene base oil; a boronated ashless dispersant; an antioxidantcomposition comprising at least one hindered phenol antioxidant and atleast one alkylated diphenylamine antioxidant; and a gear oil additivepackage having an active phosphorus content of less than about 700 ppmand an active sulfur content of less than about 2.5 wt. %, wherein thegear oil lubricant composition contains less than about 0.1 percent byweight antioxidant composition based on a total lubricant composition.2. The gear oil lubricant composition of claim 1, wherein the gear oiladditive package comprises an extreme pressure agent, an antiwear agent,a rust inhibitor, a corrosion inhibitor, a defoamer, and a process oil.3. The gear oil lubricant composition of claim 1, further comprising aseal swelling agent.
 4. The gear oil lubricant composition of claim 1,wherein the composition contains from about 100 to about 700 ppm activenitrogen atoms.
 5. The gear oil lubricant composition of claim 1,wherein the ashless dispersant comprises a hydrocarbyl substitutedsuccinimide.
 6. The gear oil lubricant composition of claim 5, whereinthe ashless dispersant comprises a boronated/phosphorylated ashlessdispersant.
 7. The gear oil lubricant composition of claim 1, whereinthe first and second olefinic lubricant comprises oligomers ofalphaolefins.
 8. A vehicle axle containing the gear oil lubricant ofclaim
 1. 9. A heavy duty gear oil lubricant composition comprising: afirst olefinic lubricant having a viscosity ranging from about 80centistokes to about 150 centistokes at 100° C.; a second olefiniclubricant having a viscosity ranging from about 2 centistokes to about15 centistokes at 100° C., wherein a ratio of the first olefiniclubricant to the second olefinic lubricant ranges from about 2:1 toabout 8:1; an alkylated naphthalene base oil; a boronated ashlessdispersant; an antioxidant composition comprising at least one hinderedphenol antioxidant and at least one alkylated diphenylamine antioxidant;and a conventional gear oil additive package; wherein the gear oillubricant composition has a reactive amine content of less than about100 to about 400 ppm based on an active nitrogen content of thelubricant composition.
 10. The gear oil lubricant composition of claim9, wherein the gear oil additive package comprises an extreme pressureagent, an antiwear agent, a rust inhibitor, a corrosion inhibitor, adefoamer, and a process oil.
 11. The gear oil lubricant composition ofclaim 9, further comprising a seal swelling agent.
 12. The gear oillubricant composition of claim 9, wherein the composition has an activesulfur content ranging from about 1 wt. % to about 3 wt. % and an activephosphorus content ranging from about 250 to about 700 ppm.
 13. The gearoil lubricant composition of claim 9, wherein the ashless dispersantcomprises a hydrocarbyl substituted succinimide.
 14. The gear oillubricant composition of claim 13, wherein the ashless dispersantcomprises a boronated/phosphorylated ashless dispersant.
 15. The gearoil lubricant composition of claim 9, wherein the first and secondolefinic lubricant comprises oligomers of alphaolefins.
 16. A vehicleaxle containing the gear oil lubricant of claim
 9. 17. A thermallystable gear oil lubricant composition, comprising: a first olefiniclubricant having a viscosity ranging from about 80 centistokes to about150 centistokes at 100° C.; a second olefinic lubricant having aviscosity ranging from about 2 centistokes to about 15 centistokes at100° C., wherein a ratio of the first olefinic lubricant to the secondolefinic lubricant ranges from about 2:1 to about 8:1; an alkylatednaphthalene base oil; a boronated ashless dispersant; an antioxidantcomposition comprising at least one hindered phenol antioxidant and atleast one alkylated diphenylamine antioxidant; and a conventional gearoil additive package; wherein, with respect to thermal stability, thelubricant composition has a carbon varnish rating of greater than about7.4 and a sludge rating of greater than about 9.3 after an L60-1oxidative stability test of about 300 hours.
 18. The gear oil lubricantcomposition of claim 17, wherein the lubricant composition has aviscosity rise of less than about 100%.
 19. The gear oil lubricantcomposition of claim 17, wherein the gear oil additive package comprisesan extreme pressure agent, an antiwear agent, a rust inhibitor, acorrosion inhibitor, a defoamer, and a process oil.
 20. The gear oillubricant composition of claim 17, further comprising a seal swellingagent.
 21. The gear oil lubricant composition of claim 17, wherein thecomposition has an active sulfur content ranging from about 1 wt. % toabout 3 wt. % and an active phosphorus content ranging from about 300 toabout 700 ppm.
 22. The gear oil lubricant composition of claim 17,wherein the ashless dispersant comprises a hydrocarbyl substitutedsuccinimide.
 23. The gear oil lubricant composition of claim 22, whereinthe ashless dispersant comprises a boronated/phosphorylated ashlessdispersant.
 24. The gear oil lubricant composition of claim 17, whereinthe first and second olefinic lubricant comprises oligomers ofalphaolefins.
 25. A vehicle axle containing the gear oil lubricant ofclaim
 17. 26. A method of operating a vehicle containing a drive axle,comprising providing as a lubricant for the drive axle a compositioncontaining: a first olefinic lubricant having a viscosity ranging fromabout 80 centistokes to about 150 centistokes at 100° C.; a secondolefinic lubricant having a viscosity ranging from about 2 centistokesto about 15 centistokes at 100° C., wherein a ratio of the firstolefinic lubricant to the second olefinic lubricant ranges from about2:1 to about 8:1; an alkylated naphthalene base oil; a boronated ashlessdispersant; an antioxidant composition comprising at least one hinderedphenol antioxidant and at least one alkylated diphenylamine antioxidant;and a conventional gear oil additive package; wherein the lubricantcomposition has an oxidation stability in a 300 hour L60-1 oxidativestability test that provides a viscosity increase of less than about100%, a carbon varnish rating of greater than about 7.4 and a sludgerating of greater than or equal to 9.3.
 27. The method of claim 28wherein the vehicle is operated in an environment having a temperatureof greater than about 40° C.
 28. The method of claim 28 wherein thevehicle is operated for a distance of more than about 30,000 kilometersbetween lubricant drain intervals.
 29. The method of claim 28 whereinthe axle is an axle of a heavy duty truck vehicle.
 30. The method ofclaim 29 wherein the heavy duty truck vehicle can pull combined loads inexcess of 25 metric tons.